1. Field of the Invention
This invention relates to electronic circuitry technology, and more particularly, to a tristate startup operating mode setting device which is designed for use in conjunction with an electronic circuit unit, such as a chip module, for providing the chip module with a tristate startup operating mode setting function that is capable of setting the chip module to a user-desired operating mode at startup by connecting an external pad in three different ways.
2. Description of Related Art
Chip modules are typically provided with one or more external pads so that the user can connect these pads in various different ways, such as connecting the pads with pull-high resistors or pull-low resistors. If the pad is connected to a pull-high resistor, it will cause the generation of a logic-HIGH signal (representative of a binary signal 1) for the chip module at startup after power-on; and whereas if the pad is connected to a pull-low resistor, it will cause the generation of a logic-LOW signal (representative of a binary signal 0) for the chip module. The generated logic-HIGH or logic-LOW signal is then used to set the chip module to a specific operating mode after power-on.
By the prior art, each pad is capable of assuming 2 output states for the operating mode setting function. Since one single pad is able to assume 2 output states for the operating mode setting function, the provision of 2 pads on the chip module will be able to assume 2*2=4 output states, the provision of 3 pads on the chip module 10 will be able to assume 2*2*2=8 output states, and so forth.
In practical applications, however, there may exist a need for 3 output states for the implementation of a tristate operating mode setting function. By the prior art, however, since each single pad can only be used to assume 2 output states, it requires the use of at least 2 pads to provide 4 output states, and from which 3 of the 4 available output states are selected for the implementation of the desired tristate operating mode setting function. One drawback to this solution, however, is that it would increase the number of pads on the chip module and therefore undesirably occupy more layout space on the circuit board.